The invention relates to the field of communication networks and more particularly radio communication networks, notably the mobile radio communication networks of the UMTS type.
More precisely, the invention relates to the use of frequency bands by user terminals for the purpose of accessing services that do not require a backward channel such as for example the broadcast services offered by such radio networks.
In this instance, “a service not requiring a backward channel” means any one-way service of the point-to-multipoint or point-to-point type, and notably broadcast services, if necessary of multimedia content, such as for example, and not limitingly, the broadcast service of the MBMS (“Multimedia Broadcast/Multicast Service”) type.
Note that the MBMS broadcast service is defined in version 6 (or “release 6”) of the 3GPP (“3rd Generation Partnership Project”) specifications, which governs the transmission of multimedia data in mobile (or cellular) networks of the UMTS type having a radio access network, for example of the UTRAN (“UMTS Terrestrial Radio Access Network”) type or of the UTRAN upgrade type, and in particular in the 3GPP technical specifications TS 25.346 and 23.246 (notably accessible on the 3GPP website at address “www.3gpp.org”).
Furthermore, “multimedia content” in this instance means data files, such as for example audio files or video files, or television programs, notably.
As those skilled in the art know, the 3GPP organization recommends two radio access network modes for mobile networks such as the UMTS.
A first mode relates to the radio access networks called FDD (“Frequency Division Duplex”) or WCDMA (“Wideband Code Division Multiple Access”), that is to say those which use a frequency duplex in order to transmit data. In this first mode (FDD), the mobile terminal of the user (or the user terminal) transmits data to the radio access network on a frequency dedicated to an uplink, while the radio access network transmits data to the user terminal on another frequency dedicated to a downlink. Therefore, in order to set up, for example, a conventional voice call, the user terminal and the mobile network transmit data on both frequencies simultaneously.
The International Telecommunications Union (ITU) in 1992 allocated specific FDD frequency bands between 1920 MHz and 1980 MHz for uplinks and between 2110 MHz and 2170 MHz for downlinks, for the FDD UMTS networks. These bands are divided into frequency blocks of 5 MHz that are paired between the “uplink” and “downlink” bands.
A second mode, that is described here as an example, relates to radio access networks called TDD (“Time Division Duplex”), that is to say those that use a time duplex in order to transmit data. In this second mode (TDD), the user terminal transmits data to the radio access network on a frequency dedicated to an uplink during a given timeslot, while the radio access network transmits data to the user terminal on the same frequency dedicated to a downlink but on another timeslot. Therefore, in order to establish a conventional communication, the user terminal and the mobile network transmit data on the same frequency “alternately”.
The International Telecommunications Union also in 1992 allocated specific TDD frequency bands between 1900 MHz and 1920 MHz and between 2010 MHz and 2025 MHz for the uplinks and downlinks, for the TDD UMTS networks. These bands are divided into frequency blocks of 5 MHz that are not paired.
The UMTS operators that enjoy the allocation of FDD frequency bands exploit the latter to such a point of saturation that it becomes difficult, or even impossible, to use them in order to offer new services such as MBMS without risking interfering with other services that already use them, such as for example the conventional radio communication services. This is all the more true when the broadcast service requires a considerable quantity of radio resources, such as for example in the case of mobile television which requires a minimum bit rate of 256 kbps (kilobits per second) for each television channel for an optimal quality of service level (or a minimum bit rate of 128 kbps for an inferior quality level).
In addition, the FDD frequency bands are usually shared by several operators, so it is yet more difficult for them to offer, each on their own side, to their respective customers services (if necessary broadcast services) which, as indicated above, are large consumers of radio resources.
Furthermore, multimedia data broadcast services, such as MBMS for example, may be used on any type of UMTS radio access network (TDD or FDD). They usually comprise two broadcast modes.
A first broadcast mode called “broadcast” makes it possible to broadcast the same multimedia data in all the cells of a service zone, of the operator's mobile network, associated with these multimedia data. All the UMTS mobile terminals, complying with UMTS version 6 (which introduced MBMS) and being in this service zone, may then receive the broadcast multimedia data.
A second broadcast mode called “multicast” makes it possible to broadcast the same multimedia data in all the cells of a service zone, of the mobile operator's network, associated with these multimedia data. But, unlike the first mode (broadcast), only the UMTS user terminals complying with UMTS version 6 that are in the service zone and have taken out a subscription allowing them to receive such multimedia data may receive the multimedia data that are broadcast.
Consequently, in a given cell of an operator's mobile network, a content may be either not broadcast when this cell does not belong to the service zone associated with the broadcast of the content (multimedia data), or be broadcast to all the user terminals situated in said service zone (in broadcast mode), or else be broadcast only to a portion of the user terminals situated in said service zone (in multicast mode).
When a content (if necessary multimedia) is broadcast in a cell, two situations may arise. The first situation usually corresponds to a situation in which a small number of user terminals receives the content. In this first case, dedicated radio channels of the point-to-point (or PTP) type are set up between the operator's radio access network and each user terminal situated in this cell and concerned with the content. The second situation usually corresponds to a situation in which a high number of user terminals receives the content. In this second situation, a shared radio channel of the point-to-multipoint (or PTM) type is set up between the operator's radio access network and all the user terminals situated in this cell and concerned with the content.
To make it easier to use the shared radio channel of the point-to-multipoint type (the second situation), the user terminals complying with version 6 of the UMTS standard receive only on a downlink the data (in the form of radio signals) that are associated with the MBMS service and that originate from the operator's radio access network. They therefore transmit no data (or no radio signal) associated with the MBMS service on an uplink. The broadcast is then said to have no backward channel. Consequently, when the radio access network is of the FDD type, the FDD frequency band dedicated to the FDD uplinks is not used by the user terminals for the MBMS service, and when the radio access network is of the TDD type, the timeslot dedicated to TDD uplinks is not used by the user terminal for the MBMS service.
To improve the situation, and alleviate the disadvantage of “overuse” of FDD frequency bands, it would be possible to fit the user terminals and the radio access network equipment with hybrid, for example FDD/TDD, transceivers. But that would be costly not only for the equipment makers (manufacturers of radio access networks and/or user terminals) but also for the operators of the mobile networks. Another solution would consist in having a mobile network operator deploy two radio access networks, one operating in FDD mode and the other operating for example in TDD mode, and in proposing that the customers of this operator buy two user terminals, one having a transceiver operating in FDD mode and the other having a transceiver operating in TDD mode so that they can receive the MBMS content. But, this solution is also costly.
No known solution is therefore entirely satisfactory.
The invention makes it possible to improve the situation by proposing to transmit certain data frames of the FDD type on downlinks of a radio access network of the FDD type to user terminals equipped with an FDD transceiver, in other available frequency bands, such as for example in at least a portion of the TDD frequency bands (that is to say at least one block of frequencies of 5 MHz in an exemplary embodiment).